I.
Introduction

Nothing
is accomplished without energy, and while the amount of energy you have
isn't necessarily as important as what you can do with it, knowing how
much energy is available is rather important to have a rough idea of
what might be possible. To be sure, with science fiction
there are tools that allow for extraordinary "cheats". Just
as a mathematically-inclined caveman might find it incomprehensible
that twitching one's finger could possibly result in a kinetic energy
of over a kilojoule capable of killing a man, Dirty Harry (with his
trigger-finger twitchy and ready) would view it as a reality of his
day-to-day life. Similarly, faster-than-light travel demands
that somehow, the space-hopping characters we watch are able to violate
relativity's demand that mass reaching lightspeed requires infinite
energy, reaching lightspeed and beyond without infinite energy input.
Cheats are just part of the game, and while it's best
to avoid assuming cheats without proof, sometimes you've just got to
admit that the rules have been broken.

The point, of course, is that when
it comes to one's power generation technology, how much energy one can
produce in a given time is not the end-all be-all criteria of
success. But having the bigger number sure doesn't
hurt. In the below, we'll take a look at the mighty cruisers
of the Empire and their reactors, so we can see for ourselves what the
true power of the Empire really is.

II.
Imperial Reactor Technology

There's been a bit of confusion
fomented over the years about just what makes a Star Destroyer
tick.
Without a whole lot of engineering details showing up in the films at
all, and with a lot of what's given about other vessels being a bit
vague or confusing (e.g. what the hell could an "alluvial dampener" be
doing on a
starship? What's the purpose of a "hydro-spanner"? Was Noah
the captain?), there's been a lot of room
for people to interject their own ideas. Early
ideas on Star Wars gave the vessels fusion-based power systems, but as
the tech inflation of Star Wars in the Expanded Universe has progressed
over the past few years we've seen the reactor technology
'retroactively improve' into something called hypermatter, separate and
quite distinct from real-world hypermatter, that makes
even antimatter weep with inadequacy.

A.
Canon Information

Despite the EU's internal
confusion, the old Original Trilogy canon didn't change at
all.

1. Reactors

We are told the following in the ANH
novelization, at the destruction of the Death Star:

There
has been much debate about this quote,
previously discussed elsewhere. Nonetheless, the
quote clearly states that a small artificial sun has liberated its
energy. Ergo, many would argue that if the Death Star were
powered by a small artificial sun, then undoubtedly it is powered by
fusion akin to what occurs in a large, non-artificial sun, whatever
opponents of the Star Wars canon might say. That fusion is
employed among the major powers of the Star Wars universe was confirmed
to an extent by the novelization of TESB, wherein we're told about
Luke's small power generator:

"'You ready for some
power?' Luke asked Artoo, who was patiently waiting for his own form of
nourishment. Luke took a small fusion furnace from an equipment box and
ignited it, welcoming even the tiny glow thrown off by the small
heating device, then took a power cable and attached it to Artoo
[...] As power radiated through
Artoo's electronic innards, the stout robot whistled his appreciation."

Of course, just a few pages later, a bit of confusion comes
into the picture . . .

"Luke turned around to
see the little droid standing forlornly next to the miniature fission
furnace." (Ch. 8)

As seen in the film, the scenes looked like this:

Whether the unit was fission-based, fusion-based, or both, the
fact of nuclear technology being the standard is seemingly
confirmed. Of course, as with our own technology
different techniques are used for different purposes. No one
would use a tiny internal combustion engine to power their laptop, for
instance, just as we wouldn't try to stick a huge lithium battery into
an aircraft carrier to give it power. Certainly R2-D2 doesn't
seem to have a nuclear reactor on board, given that he must be
recharged by one. On the other hand, if you have
fusion power available and have perfected it to the point where you can
make huge
reactors and
tiny ones, then it's likely to be the most widely-used method
of power generation you're likely to employ, just as internal
combustion is for us today.

"Children on Tatooine
tell each other of the dragons that live inside the suns; smaller
cousins of the sun-dragons are supposed to live inside the fusion
furnaces that power everything from starships to Podracers."

That suns and power generators are both fusion-based
is thus
made very explicit by the narrator, even accounting for the imaginative
dragon infestation that the children tell each other about.
Given
that at least one child on Tatooine had the engineering skills and
know-how to race and build podracers along with his friends, the claim
opponents of the canon make that these are the deluded ravings of
sugar-mad uneducated children is absurd. Thus, barring some unmentioned
change in the intervening 20 years, a Star Destroyer runs on fusion
just as much as Clone Wars vessels did.

Happily,
we even get to see the "engine
room" of a Clone Wars-era Republic
Venator, the Tranquility. Given that these vessels were the
earliest Imperial
Star Destroyers (as seen at the end of Revenge of the Sith),
it is likely that
Imperial Class Star Destroyers of two decades later shared similar
design philosophy. The room is
extraordinarily large and empty, several decks tall and dozens of
meters wide.

Note at right the tiny
Ventress looking down at the spotlight-eyed droid on the walkway.

Although we could presume that
this is to allow some sort of high-pressure leak a lot of expansion
room, the fact that plain old air vents are present in the room with no
apparent closing mechanism (merely a grate) suggests that, instead,
this empty space is there for some other purpose. Perhaps
some
sort of higher density leak could settle to the bottom, or perhaps the
extra distance from the machinery allows some sort of radiation
shielding that is sufficiently lightweight to offset the extra volume,
whereas a smaller volume would require heavyweight cladding.

Whatever the
case, the cavernous room is home to three columns with spherical
objects atop separate
pedestals. At the floor of the room is a large hemispherical
object, with another on the ceiling. It is not clear what
items are the reactors for the ship. When charges were placed
around the Tranquility engine room
and detonated,
crippling the ship, one of the three spherical objects appeared to fall
over completely or was otherwise heavily damaged. However,
while the room did have continuing
fires, at no point was there any mention of a possible reactor overload
as has been made to occur when other reactors have been attacked with
explosives (e.g. "Weapons Factory"[TCW2] or the Death Stars).
Presumably, then, the three spheres are not, themselves,
reactor cores.

Star Wars reactors
commonly feature a top hanging part and a bottom part with a skinny
connection between them, plus a whole lot of extra space around them.
Note the Death Star II reactor chamber, the Geonosian droid
foundry reactor from "Weapons Factory"[TCW2], and similar.

Further, the ship was apparently repaired fairly quickly
after the situation ended. Other vessels have not been so
lucky. After a power
surge caused explosions throughout a battle-damaged Separatist
Munificent in "Cargo of Doom"[TCW2], the
vessel's "main
reactor is exposed", per Admiral Yularen, and
it "will
implode at any moment". This may suggest
certain
things about the sort of reactions involved, since a fusion reactor as
we understand it that is suddenly 'open to the public' would disable
itself quickly, rather than destroy itself and its surroundings.

Instead, Yularen's comment and the other
similar
reactor-blowing incidents suggest that Imperial fusion technology is
based around some remarkably unsafe design (even for fusion).

2. Generators

On Naboo, a very different device is present, referred to as a
generator for the power station. Long tendrils of a white
glowing plasma within some sort of tubes criss-crossed a massive
chamber with the usual unsafe Star Wars walkways, and a ray-shielded
room with a seemingly bottomless pit (described in the script as the
melting pit) sat nearby. The location was described in the
novels:

"
They were in the service corridor for the melting pit, the disposal unit of
the power station's residue. The service corridor was armed with lasers
against unauthorized intrusion." (TPM Ch. 22)

"
He sometimes dreams of when he was a Padawan in fact as
well as
feeling; he dreams that his own Master, Qui-Gon Jinn, did not die at
the plasma-fueled generator core in Theed." (RotS Ch. 1)

This power generator would likely be a generator of the type
we know
of, one which converts energy from one form to another. Thus
the
plasma, from whatever source, is being converted into electrical power
here. But, then, what a melting pit would be doing there is
unclear, since it is uncertain what sort of residue would be created by
a plasma-fueled generator.

Perhaps the plasma is from a
fission reactor, and the melt pit is a way of dumping radioactive
waste? But that hardly seems safe on a planet with such vast
underground water habitats. So the design and technology of
this
generator is somewhat confusing.

B.
Discussion

The reason for fusion's safety is
that it
requires extreme temperature and pressure to be initiated and
continued. A runaway fusion reaction within a reactor is thus
considered largely impossible with even the most simplistic safety in
the design, since a constant stream of fuel and constant powering of
the confinement system (magnetic, laser, or what-have-you) is required.
As soon as a fusion reaction got too 'hot', then, it would
either
activate automatic cutoffs or simply destroy what was keeping the
reaction going.

However, it is conceivable
that there are specific types of fusion or fusion reaction chambers
that might allow for extremely efficient reactors which, as a drawback,
can somehow suffer from runaway reactions. For instance,
liquid
lithium is currently used as a coolant and tritium breeding
ground
in many of our designed or experimental reactors, and lithium is also
potentially useful as a fusion fuel directly. One can thus
imagine a coolant leak into the reactor core producing significant
unplanned fusion events, potentially, though in most current designs
this would be virtually impossible . . . it would be more like dousing
a fire with water than throwing gasoline on it. However, it
is
at least conceivable that a high-volume and less-safe design might have
risks of this or a similar nature.

1. Fusion Reactions

As far as what we know
of fusion now, "simple" deuterium-deuterium fusion reactions
require millions of degrees and incomprehensible pressures to get
started and to be maintained. Once going, however, the
reaction
produces a Helium-3 atom, a stray neutron, and an energy of
3.27 megaelectron-volts (MeV). A single joule is equivalent
to
6.24 quintillion eV, or 6.242E18 eV, but
given how many atoms are involved per gram the energy involved adds up
rather quickly!

Just as likely for the reactants
above, however, is a
result of a tritium atom plus a normal hydrogen atom, along with 4.0
MeV. So assuming both occur with about a 50% chance then you
end up with four deuterium atoms (deuterons), a helium-3, a tritium, a
hydrogen, a neutron, and a boatload of energy. But with
fusion afoot, those reaction products can also be made to fuse if the
temperature and pressure is there, in which case one ends up with even
more energetic deuterium-tritium reactions along with a reaction
between deuterium and helium-3. All around, then, one ends up
with 2 helium-4s, a normal hydrogen atom, a couple of neutrons, and an
energy release of 43.2 MeV from six deuterons. This is one
possible fusion cycle
. . . a planned series of fusion events occurring in the correct order
to more efficiently make use of reactants and reaction products for
maximum energy production.

Of course, there would be the issue
of those pesky leftover neutrons. One can hardly imagine
Palpatine and
the senators standing around at the end of Attack of the
Clones like there wasn't a problem in the world if they were
being bombarded by neutron and secondary gamma radiation from the
Acclamators as they were taking off. However, there would be
ways to
mitigate the radioactivity. For example, neutrons
can be readily absorbed by light nuclei like
hydrogen. Thus cheap, plentiful substances with a
significant amount of hydrogen per unit mass like water, concrete (high
in water content), polyethylene, or something like paraffin wax are
useful neutron absorbers.

2. Tackling the Neutron Problem

An alternative would be a type of
fusion that does not result in such
large amounts of neutron radiation. Various concepts for such
aneutronic fusion have been proposed. One involves deuterium
and
helium-3. Using deuterium and helium-3 only
results in run-of-the-mill helium-4 and a proton, unleashing 14.7MeV,
and while other reactions could occur (such as deuterium-deuterium)
that would still result in some neutron radiation, the levels would be
significantly lessened (aneutronic reactions are defined
as reactions where less than 1% of the energy produced is carried off
by neutrons). There is the problem of the extreme temperature
requirements of deuterium and helium-3 reactions (some ten times
greater than D-T reactions), but this can be lessened with
significant pressures. Suffice it to say that there's a bit
of a
startup problem involved.

Another alternative,
considered implausible for modern Earth due to fuel availability, is
helium-3
fusing with helium-3. However, helium-3 is abundant in the
solar
system, with vast quantities of it on the surface of the moon needing
only heating to release, or minable from gas giants. It also
releases a bit less energy than deuterium and helium-3.
Helium-3
and Lithium-6 is a bit better than both, but less impressive than the
cycle mentioned first.

Carbon
also has a unique fusion cycle known as the CNO cycle, commonly though
to be the power source of stars larger than our sun. It is
workable at
15
million K and above, soaking up free protons in the reactor
and spitting out hydrogen, helium, positrons, and
neutrinos. The cycle is fairly energetic,
outputting 26.72 MeV for a full cycle, but it involves a significant
startup penalty.

3. The Steam Question

One possible reason for all the
water-related terms (e.g. "alluvial
dampener") is in relation to the fact that there's an
awful lot of steam in Star Wars. The generator on Naboo had
bursting steam pipes near the melting pit, per the novelization.
The droid foundry on Geonosis in Attack of the Clones had
enormous steam exhaust vents, and if we are to assume that like the
droid foundry of "Weapons Factory'{TCW2] and the AotC version are
similar then both had their own reactors. The hangar of the
Invisible Hand is said, in the RotS script, to have extensive steam
piping. The rebel base on Hoth had broken steam
pipes, per the script and TESB novelization, and Cloud City seemed to
be full of steam in the engineering areas. The Return of the
Jedi script and novelization features a boiler room in Jabba's palace,
with the latter describing "deafening machine sounds - wheels creaking,
piston-heads slamming, water-hammers, engine hums -and a continuously
shifting haze of steam", and when on the Death Star II the situation
turns against the Empire, the chaos is described as "Electrical fires,
steam explosions, cabin depressurizations, disruption of
chain-of-command."

It is not at all clear what all
that steam is doing around. It's possible that, just as naval
aircraft carrier plane-launching catapults use steam generated by the
reactor to push a plane into the air, steam is used in the Empire for
other similar purposes. Heating would be a possible choice,
but given that Palpatine was hanging on to the hangar steam pipes by
hand then heat radiation was clearly not the goal. Whatever
the case, steam technology was presumably enough of a requirement that
Jabba's palace featured a boiler room. While this might've
been intended to simply give the palace a more skin-friendly humidity
level than might be found naturally on Tatooine, that's not at all
obvious given the heavy machinery and large room involved.

It seems plausible that in addition
to electrical wiring, simple steam is used for some purposes, though it
isn't clear what.

C. Conclusion

Given the millenia of technological advancement
of Star Wars, I feel quite certain they're capable of virtually any of
the more
efficient means of fusion, and have probably developed ways of keeping
the radioactivity a virtual non-issue. However, in spite of
this concept, it is clear
from
the canon that their reactor designs, however efficient they may be,
introduce some deleterious safety concerns.

III.
Fuelling the Reactors

As established, even children on Tatooine know that fusion
powers everything from podracers to starships. We
would thus expect that any mention of the fuel for these vehicles would
probably involve ultra-cold or highly-pressurized deuterium, or perhaps
metal hydrides capable of storing hydrogen more easily and compactly,
or similar. Other possibilities also exist, such as the
new
idea of storing hydrogen in carbon nanotubes and other solid
carbon forms, achieving a result similar to the metal hydrides but with
more efficiency in terms of volume and weight.

One might expect some indication of one of these sorts of
techniques. But instead, while we do get mentions of the fuel
these vehicles work with, it in no way resembles what we might expect
from the list provided above.

A.
Canon Information

Let's start with this
description of podracing from Chapter 1 of the TPM novelization:

"All that power, all that
speed, just at his fingertips, and no margin for error. Two huge
turbines dragged a fragile Pod over sandy flats, around jagged-edged
mountains, down shadowed draws, and over heart-wrenching drops in a
series of twisting, winding curves and jumps at the greatest speed a
driver could manage. Control cables ran from the Pod to the engines,
and energy binders locked the engines to each other. If any part of the
three struck something solid, the whole of the assembly would collapse
in a splintering of metal and a fiery wash of rocket fuel."

It's those last two words that are of interest . . . "rocket fuel".
Of course almost anything can be rocket fuel, but here we're looking
for something that is liquid and flammable, given the "fiery
wash". Liquid deuterium qualifies, but only to the extent
that, as it boils upon exceeding 20 K, flammable hydrogen gas is
produced, a gas that very much likes to combine with oxygen.
The description above is more suggestive of flammable liquid.
Of course, it's possible that the podracer's electrical
systems
are powered by fusion whereas the engines use a separate fuel, but why
keep a fusion reactor on the pod when it could simply sip a tiny bit of
power from the engines, as a modern fighter might?

A few other consistent mentions of such fuel appear in TPM
regarding podracers. Elsewhere, observe the mention of fuel
as carried aboard a snowspeeder in the text from Chapter 6 of TESB
below:

"At that instant,
Hobbie's burning ship crashed through the walker cockpit like a manned
bomb, its fuel igniting into a cascade of flame and debris."

Here again we have behavior which could be basically on par
with modern-day
petroleum-based jet- or rocket-fuel. Fighters are referred to
similarly in Chapter
12 of ANH:

Hydrogen gas without oxygen does not burn, but some rocket
fuels will. Similarly, RotJ's ninth chapter gives us the
following:

""Father, I won't leave
you," Luke protested. Explosions jarred the docking bay in earnest,
crumbling one entire wall, splitting the ceiling. A jet of blue flame
shot from a gas nozzle nearby. Just beneath it the floor began to melt."

While there's no specific statement on what the gas nozzle was
normally used for in the small vehicle landing bay, the implication of
a refueling port is quite tempting, if not altogether likely given the
usual hose-based refueling systems used for fighters.

So what's really going on here? Is there some sort
of contradiction afoot? Does the mention of fusion
in RotS suggest different
technology than used elsewhere?

Well, no. The same fellow who wrote about fusion
furnaces, after all, was writing from a script containing the following:

12
INT. GENERATOR ROOM -- TRADE FEDERATION CRUISER

The
TWO JEDI cut their way down several floors into a large generator
room. Huge EXPLOSIONS outside the ship have caused several
large pipes overhead to break, and fluid is spewing
everywhere. The Jedi get up and turn off their
lightsabers. ANAKIN dips his hand into the fluid and sniffs
it.

Obi-Wan:
. . . fuel. The slightest charge from our sabers will send
this ship into oblivion. That's why they've stopped shooting.
Anakin: Well, then, we're safe for the time being.
Obi-Wan: Your idea of safe is not the same as mine.

They
run, EXPLOSIONS rattle the ship, and pipes continue to burst around
them, spilling more fuel into the hallway. At the far end,
SIX SUPER BATTLE DROIDS drop into the fuel. The SOUNDS OF
SHIELD DOORS CLOSING AND LOCKING ECHO throughout the hallway.
They pass several large power generators, which are topped with
SPARKING excess power dischargers.

THEY
move along a wall. ANAKIN climbs up the side to a small
vent. The fuel gets closer to the SPARKING dischargers.

Obi-Wan:
We'll never get through that. It's too small!

They
move toward a second vent. OBI-WAN is swimming in the fuel as
it reaches to within a couple yards of the ceiling. ANAKIN
feels along the ceiling and finds another smaller vent. He
closes his eyes and tries to sense an opening, then he moves
on. OBI-WAN is forced into hand-to-hand combat with one of
the SUPER BATTLE DROIDS. It pulls the Jedi under the
fuel. Just before he is about to drown, OBI-WAN disables the
SUPER BATTLE DROID by pushing him into an exhaust pipe.
The fuel is up to the Jedi's chins. ANAKIN finds a very, very
small metal grate, then pounds on it until the tiny grate breaks loose.

Anakin:
I found our escape vent.
Obi-Wan: Anakin, this is no time for jokes. We're
in serious trouble here.
Anakin: Only in your mind, My Master. Look, no
structure. . . .

ANAKIN
grabs the side of the tiny hole and gives it a big yank, ripping a
large panel loose revealing a "man-sized" work shaft. They
scramble through it as the DROIDS swim closer.

13
INT. VENT SHAFT -- TRADE FEDERATION CRUISER

The
TWO JEDI pull themselves through the narrow vent shaft until they reach
a small hatch in the side of the tube.

Anakin:
Here's a way out.

As
the SUPER BATTLE DROIDS reach the opening in the ceiling and the fuel
gets to within a few feet of the power generator sparks, the JEDI work
the keyboard on the pressure lock, opening the hatch.

14
INT. SMALL PASSAGEWAY -- TRADE FEDERATION CRUISER

The
TWO JEDI climb into a small passageway and slam the hatch
shut. They make their way through the ever-shrinking shaft
until they reach the end.

15
INT HALLWAY -- TRADE FEDERATION CRUISER

A
hatch opens in one of the main hallways of the Trade Federation
Cruiser, and the JEDI squeeze out, SLAMMING the hatch. Behind
them, ANAKIN seals the hatch with his laser sword.

Obi-Wan:
That won't hold when the fuel hits those power dischargers.
Anakin: The blast will break the hull. This side's
pressurized.
Obi-Wan: You still have much to learn, Anakin.

16
INT. VENT SHAFT -- TRADE FEDERATION CRUISER

The
SUPER BATTLE DROIDS climb up the vent shaft. SUPER BATTLE
DROID R77 and SEVERAL OTHER DROIDS wait in the generator room as the
fuel continues to rise toward the power discharger.

Super
Battle Droid R77: I have a bad feeling about this.

17
INT. GENERATOR ROOM -- TRADE FEDERATION CRUISER

The
fuel hits the SPARKING power discharger, and there is a HUGE EXPLOSION.

18
EXT. TRADE FEDERATION CRUISER -- BATTLE

A
GREAT EXPLOSION and a flaming gas cloud spray out of the side of the
Federation Cruiser.

19
INT. HALLWAY -- TRADE FEDERATION CRUISER

A
large bulge appears in the wall around the sealed hatch as the
EXPLOSION hits. OBI-WAN jumps back, then stands amazed.

Obi-Wan:
All right, you win. I have much to learn. Let's go!

ANAKIN
grins at OBI-WAN, and they run down the hallway.

The above makes it clear that we're dealing with liquid fuel
for the cruiser Invisible
Hand, obviously, just as liquid fuel seems to be the norm
for other fusion-powered Star Wars vehicles. So instead of a
contradiction, we need to figure out how one would store hydrogen in a
liquid form.

Happily, we may
have a name for this fuel, whatever its precise composition.
In
"Rookies"[TCW1], a "highly explosive" liquid fuel called tibanna is
used as a heating fuel for a base. And, similar explosive
fuel
cells have been seen elsewhere, such as one of the landing bays of the
listening post from "Duel of the Droids"[TCW1]. Barring a
separate and distinct type of fuel, then it seems that this might be
the fuel we're looking for.

As it happens, we've heard of
tibanna before. Cloud City on Bespin from TESB was a tibanna
gas
mining facility, meaning that tibanna is a naturally occurring
material. The idea of tibanna gas being on Bespin might give
us
pause. If Cloud City was floating amongst tibanna gas then
why is
it a liquid elsewhere? However, this is not likely to be an
actual issue. First, just as water can be a vapor or liquid,
tibanna might be in vapor form for the most part on Bespin.
Second, given the fact that weapons fire and ship's engines
did
not seem to be an issue near Cloud City, it seems likely that the
tibanna gas was elsewhere in the atmosphere, presumably at lower depths
or in particular cloud formations. As a result, tibanna might
likely be a liquid in its natural form and Earth-normal atmospheric
conditions.

In any event, though, we can tentatively say that
this liquid tibanna may be the power source for most Star Wars
technology, whether via combustion for rocketry or fusion for energy.

B.
Discussion

Could
tibanna be a Star Wars galaxy term for something we know?
After
all, if we roll with the concept of a liquid that has a lot of hydrogen
in it, then we already know of more than a few possibilities today.

1.
Fuel Properties

Whether in
the form of alcohols like ethanol or methanol, or in the form of a
compound like ammonia, or in the form of hydrocarbons such as gasoline,
or in the form of water, liquid containment of hydrogen is not a new
idea. And while new methods of storing deuterium in
a liquid form may appear in the years to come, we can try to take known
liquid storage mediums and apply what we know from the Star Wars canon
to try to get a rough idea of what the most likely type of liquid
storage
medium might be.

a.
Requirements and Possibilities

First, let's ponder the requirements we have so far:

1.

Per the explosion of the
Invisible Hand described in the script, the flame of the liquid when
combusting must be visible, per the RotS script.

2.

The vapor of the liquid must
have a high flash point, given that the liquid itself had to reach the
sparky-thing in the RotS script before the explosion
occurred. If the vapor is significantly heavier
than air, the same result is achieved. Mileage may vary here.

3.

The liquid must be
sufficiently volatile (i.e. evaporative) that it evaporates fairly
quickly, given that the
fellows looked dry later on.

4.

The liquid must have a
distinct odor, but not an especially pungent one. Anakin had
to dip his hand in it and sniff, as opposed to many fuels which can be
smelled from a great distance.

5.

The liquid must not be
poisonous or especially dangerous on contact with skin or
eyes. Minor irritants are allowed (see note following).

6.

The liquid must be such at
near-room temperature . . . no cryogenic liquids like liquid hydrogen.

7.

The liquid must be
transparent or semi-transparent, given the hand-to-hand combat that
occurs (and which, clearly, we would've seen had these scenes been
shown).

8.

Preferably, the other
elements involved should not interfere too much with the fusion
process. Of course, since the deuterium-tritium part of the
deuterium cycle discussed above requires a temperature of no less than
40 million K at high pressure, this probably isn't too much
of a problem.

9.

Preferably, for
use as rocket fuel in space, a separate oxidizer should not be
required. Or, in the event that pure rocket thrust is not the
use
of the fuel, it should be usable as propellant in an ion engine.
Or both.

As an aside, it's really quite wonderful that we have so much
information. Rarely, and especially rarely in Star Wars, do
we
get such useful information about anything. However, these
requirements knock out several possibilities.

Heavy water (D2O) containing deuterium
in the place of hydrogen, for instance, is right out, thanks to it
having all the flammability of . . . well, water.

Nitrogen and hydrogen combinations don't work well for us.
Pure ammonia (NH3) is a gas at room
temperature and is quite odiferous and irritating even in low
concentrations, such as when mixed with water in household cleaners
which commonly feature only 5-10% ammonia. While some
additive might negate these effects, But it would've
worked nicely otherwise, given that its properties make it a very good
coolant as well. Hydrazine (NH4) or
UDMH (C2H8N2)
are highly toxic.

Hydrogen peroxide (H2O2)
is a monopropellant (i.e. requiring no separate oxidizer, since it is
one), but it is not flammable by itself and is highly toxic in pure
form.

Most alcohols are also out. Our good friend ethanol
(C2H6O) is a severe eye
irritant and readily evaporates in pure form, leading to flaming
beverages and, more to the point for our purposes, a risk of vapor
combustion in regards to the sparky thing in the Invisible
Hand.

Which is a damn shame, really,
because there's absolutely nothing better than the notion of a
booze-powered starship. Except that you can then drink
yourself into an engine shutdown.

Methanol (CH3OH), like hydrogen, burns
almost invisibly, and suffers other failings that ethanol has.

Most other alcohols are also troubled. Cyclohexanol
(C6H11OH) is great for
most of our purposes, except for the severe eye
irritation. Mitigating substances might help here,
or else mixing in water.

On the other hand, there are alkanes which are similar, but
simpler. Cyclohexane (C6H12)
works just as well as cyclohexanol. Some heavier alkanes also
work.

At this point, though, we're simply dealing with hydrocarbons
. . . the same sort of materials that we've been burning for centuries,
whether in the form of paraffin for candles or gasoline and jet fuel
for our spiffiest toys.

2.
StarfleetJedi.Net and the Diesel Starship Argument

The problem we face in attempting to select a suitable
known substance is that we could use many possible substances (and
combinations or variations thereof) that meet most of our
needs. Another researcher addressing the topic decided that
the best response was to simply make a choice . . . one not necessarily
without irony.

Hence the concept of diesel starships
at StarfleetJedi.Net, which is as close to the coolness of a
booze-powered starship as one can get. Quoting:

"The
various references to power plants in the six movies, put together,
paint a very intriguing picture.

Fusion power is clearly the rule of the day, from starships to portable
heaters. At the same time, liquid fuel is used for both starships and
ground vehicles (the Invisible
hand, AT-STs, landspeeders, podracers, etc);
we know all these references that it is flammable.

Were it used alone
by starships,
we could
presume it to be a propellant; if
fusion power generators as small (and presumably inexpensive) as the
heater seen in TESB were viable, there would be no reason
to power an AT-ST chemically. Together, these bits of data from the
movies and their novelizations
combine to tell us that Star Wars starships run fusion engines that
fuse hydrocarbons.

{...}Water is often cited as a good method of storing hydrogen. Water
is one
ninth hydrogen by weight,
giving it a higher volumetric density of hydrogen by weight than pure
hydrogen under all normal ranges of temperature and pressure. Heavy
water, water containing deuterium instead of
"regular" hydrogen (protium), has 0.2 grams of deuterium per
milliliter.

However, hydrocarbons are even better. A "heavy" decane would have
0.225 grams of deuterium per milliliter, while being lighter than heavy
water, less corrosive, more compressible under sudden shock; it doesn't
expand when it freezes, bursting pipes and tanks; it has over
twice the temperature range that it stays liquid in. All these features
make hydrocarbons a logical form to store hydrogen in.{...}

To put it simply, Lucas has invented - intentionally or not - the
diesel starship. A raw output of 70-230 terajoules per liter (100-280
TJ/kg) is
quite enough for the purposes of any ship's actions in Star Wars."

Unfortunately, diesel fuel, like many other potential choices,
only
satisfies some of the requirements and preferences we have for the
fuel. However, it is a captivating idea, and is close to
what we
need.

C.
Conclusion

Is diesel close enough to be considered 'true'? I
think
not, but it is close enough and familiar enough to make it useful as a
guide to understanding the technology.

In other words, it is
clear that whatever the fuel source used for Star Wars vessels, be it
liquid tibanna or some other substance, it is
not some strange and incomprehensible material, unknown and unknowable
to modern science, but simply an excellent hydrogen storage medium in
liquid form that also makes a good rocket fuel. Understanding
it
in terms of diesel or gasoline or similar petrochemical fuels, with
suitable caveats, does give the proper flavor of its
qualities.

But frankly, I'd still prefer a ship powered by vodka.

IV.
Reactor Power Requirements

Not much is known about the power requirements of a Star
Destroyer. Effective
values are abundant and can be useful for comparison, but these do not
tell us anything
about the actual reactor power . . . only the effect of the particular
technology
being examined.

For comparison, however, let's stop and ponder a modern
aircraft carrier. The USS Enterprise (CVN-65) has eight
separate model A2W nuclear reactors on board. All such naval
reactors generally operate the electrical systems of the
boat via steam-fed generators, as well as turning the screws.
Direct ratings are hard to come by, given that telling
everyone the weight and horsepower of your boat is about the same as
giving the speed, which of course is classified information.
However, some data is out there.

Later carriers such as the Nimitz Class feature two reactors
of the A4W type, rumored to have an output of around 100MWe
each (that's not the direct thermal output of the reactor, but the
usable energy after conversion (e.g. to motion or electricity). The
next generation carrier and its two reactors are planned to rate 300MWe
each, for a ship output of 600MWe . . . starting
to encroach on gigawatt territory. Given the inefficiencies
in recovering the energy from the reactor with modern technology, the
reactors themselves probably run at at least a gigawatt, if not more.

A suitably complex calculation based on the ship's mass, water
displacement and hull shape, and known (or guessed) maximum velocity
and other matters could provide a workable estimate of the usable
output of the Enterprise or Nimitz reactors.

However, we must be cautious before leaping to the conclusion
that we can do the same thing for Star Wars ships. After all,
the modern space shuttle does not have a reactor powering her engines.
A shuttle's
primary electrical
power comes from a series of fuel cells while her main engines and
orbital maneuvering jets use completely separate energy sources (i.e.
rocket fuel). Or, for a completely opposite example, the sailing
ships preceding aircraft carriers were propelled not by onboard
sources, but by the winds of the world.

Indeed, it
is a widely held assumption in science fiction and especially certain
sectors of Star Wars technological analysis that for any event we see a
ship perform, the effective energy required must have been provided by
the reactor directly. Thus, even for technology known to
'cheat',
the reactor is claimed to have the requisite energy to have performed
the task anyway, and this level of energy is then assigned to other
tasks. This would be akin to assigning Dirty Harry's
trigger finger the requisite strength to flick a bullet and give it a
kinetic energy measured in kilojoules, and from there determining his
running speed. It just doesn't work.

Thus, we must be cautious in attempting to assess or assert
reactor power requirements.

A.
Canon Information

Canon
information on the actual power requirements for Star Wars ships is
perhaps even more complicated than getting information for Earth naval
ships. There are many things we could try to
calculate
from, but if we look closely none of them are guaranteed to offer any
sort of direct
relationship as we might've thought at first. In
order to figure out a reactor
power output, it takes that direct relationship.

1.
Firepower

For instance, we could calculate based on the idea that the heaviest guns of a
Star Destroyer are probably
capable
of shots yielding as much as 1.5 megatons. It's a laser, right,
so they had to power it, right? Unfortunately, no. Star
Wars weapons are not lasers, but are instead based on
something called a "galvened
particle beam",
where "galven" is a nonsense
word. And, as seen in RotS, the particles or power or both of the bolts
are apparently supplied to the broadside gun . . . one type of weapon
used shell casings like that of a bullet, and we can assume that other
weapons not using shells simply had some sort of tank or piping
arrangement involved. As noted in the ANH script, the guns
"wind up their turbine generators to create sufficient power", belching
smoke in the process. While reactor energy is no
doubt important in accelerating the particle beams (and maybe even
doing the galvening, whatever that is), there's no way to get any
useful reactor power estimate from that. (To put
the problem in a more modern-day context, the issue would be akin to
trying to figure out the amount of fuel oil burned by a WW2 Iowa Class
battleship by calculating the energy involved in firing a full
broadside of shells, shells which were propelled by a type of gunpowder
charge in a bag. The direct relationship of shot and fuel
consumption just isn't there.)

2. Shields

Shields have also been suggested as a way of deriving reactor
energy, but here too we meet problems. How do we consider
shields to operate? Is it a direct counterforce, like
stopping a projectile with an equal projectile? Then the
shield requires exactly as much energy as it is deflecting.
Is it like a wall, stopping whatever hits it without any
input of energy? Then the shield requires only enough energy
to 'build the wall', however much that might be. Is it like
a magnet, putting out a magnetic field that might deflect a projectile
without the magnet itself being powered, but merely using stored
energy? Then the shield could be charged over a significant
period of time, so there's little way to know reactor power from that.
(Had Tsar Bomba been a total release of energy stored in a
battery, then a powerful car engine could've charged it up in 31,000
years. Absurd, but it gets the point across.)

3. Reactor Overloads

Often
the result of the success of the first item or the failure of the
second, reactor overloads could also provide a gauge, perhaps. These are
generally sufficient to destroy a ship, but don't accomplish much more
than that. For instance, in "Destroy Malevolence"[TCW1] we
see
Amidala intentionally overload the "power system" of her Nubian Yacht
(of the same type, perhaps the same vessel, seen in Attack of the Clones,
and of the same type as destroyed by Jar-Jar in "Bombad Jedi"[TCW1]).
The captured vessel, commonly reported to be 40-50 meters in
length,
exploded in a pyrotechnic display with burning debris tossed about the
docking bay, but the vessel was mostly intact and there was no
evidence of any significant nuclear-scale blast effects.

Return of the Jedi also
appears to feature an ISD reactor overload.
The incident occurs during a short-range near-broadside match
against
a Mon Calamari Rebel cruiser. Two heavy Mon Cal shots miss
the ISD
completely, but a smaller third shot does hit the area of the bridge
tower at about the same time the main hull superstructure suffers a
massive explosion. The center of the ship thus in flames, the
four
portside heavy turbolaser batteries explode, followed by detonations
apparently from the ventral bulb structure and the hangar
areas
forward of that. Within two seconds almost the entire vessel
is
covered in explosion and flame, at which point the scene changes.
While the event appears quite destructive, the portside aft corner of
the ship is still visible, seemingly intact and unmoved. More
remarkably, the bridge tower and most of the superstructure beneath it
is also visible through the darker orange flames. To be sure, we
cut away so quickly that the vessel may yet have torn itself apart, but
the nature of the event strongly suggests that the ship will end up a
burning hulk rather than an
exploding mass of vapor or debris.

But
again, the problem we face is that these events are not readily
explainable. As noted, after all, fusion shouldn't involve
reactor overloads . . . the fact that it does means that these events,
however interesting, are too vague, and whatever lower limits we could get from them are probably too small to matter.

4. Antigravs

Another
option is to work from the
assumption that
an ISD
could take off from a planet and achieve orbit like its Clone Wars-era
predecessors, calculate the energy of that, and figure out the power
required to do so in a certain length of time.
However,
Star Wars vessels employ repulsorlift technology when within six
planetary diameters (ANH novel), and we don't know how that
works. People commonly imagine some box hooked to ship's power
that, when activated, acts like a rocket putting out some ethereal
unknown propellant, but there's no evidence for that. For all we
know it's some technobabble complex gravitic or
magnetic mirror or sail system needing almost no power at all, the
space equivalent to an airship flying due to helium's presence.
(Ironically, the claim that repulsors can levitate a vessel
without power input is a
position claimed by some of the same non-canon authors (e.g.
Curtis
Saxton) who so strongly proclaim extreme hypermatter power and
impregnable neutronium
hulls.)

We know it is more than a simple gravity-nullification
field since it apparently provides propulsive force based somehow on
the gravity well of the planet. Quoting ANH Chapter 7, "Antigrav
could operate only when there was a sufficient gravity well to push
against-like that of a planet {...}".

Pushing
against gravity seems quite an odd concept. Magnetic repulsion of other
magnets with suitably oriented fields is one thing, but gravity is not
known to have any repulsive qualities. Still, the mysteries of
magnetism may be a guide. For
instance, a magnet might just sit around being a magnet, but if it
is sitting atop certain ceramics that can become superconducting when
cold, then the magnet could levitate itself . . . it does so because
the superconductor is basically shielded against the magnetic field,
reflecting it in a sense. So let's turn that upside down.
If we chilled the ceramic to the appropriate temperature, it
could levitate, only doing so "when there was a sufficient magnetic
field to push against - like that of a permanent magnet." The
only energy input required would be in cooling the ceramic, but this
could be done with something like liquid nitrogen cooled off-site and
stored wtihin good insulation for later use. Far from being a
made-up example, there's a demonstration of that very thing right here, in the form of a model maglev train. Give the train a push, and off it goes just as fast as you pushed it
until the ceramic material warms to a non-superconducting state. Then
it will drop back down onto the permanent-magnet track.

Locally
. . . that is, in the context of the train which carries the ceramic
and liquid nitrogen . . . no input of electrical or heat energy is
required for maintaining levitation. Of course, what's really
happened has involved a lot of energy. For one,
cooling the nitrogen requires forced heat transfer, which requires
energy (otherwise your freezer would never need to be plugged in).
And there's the push to get it moving. And, of course, the
magnetic field of the track is what is really
doing all the levitation work . . . the ceramic superconductor is
basically just being pushed away from that field. But from the
train's perspective, it's almost a free ride.Some might even argue that the supercold liquid nitrogen is drawing
energy in from the ceramic material or train as it is heated, rather
than providing any energy whatsoever.

And
it
may not work just based on
simple
gravity fields . . . it may in part be a surface-repulsion effect,
assuming ground vehicles operate similarly.
After
all, as seen in The Clone Wars series (e.g. "Weapons Factory"[TCW2], et
al.),
repulsor-tanks with ground removed from beneath them quickly fall down
. . . the same is true even when the ground is a plasma bridge acting
as a solid surface ("Liberty on Ryloth"[TCW1]).
And yet, when Qui-Gon and Jar-Jar are under a hovertank in TPM,
they
aren't squished when they are part of the surface presumably being
pushed against, nor are those who are under the various starships seen
taking off in the films or The Clone Wars
episodes suddenly smashed. Of course, given that repulsorlifts
seem to work against gas giants (e.g. the Death Star's orbit of the
Yavin gas giant), that doesn't seem to work out.

Given
the superconducting ceramics example, one can imagine a unit containing
a material
that, when cooled or heated, exhibits unusual properties in regards to
its interaction with gravity waves or the theorized graviton particle,
until it wears out. It may take a number of these units
throughout a ship, or perhaps the
material is simply tossed into the reactor. Or, it may be that
the
material simply requires an initial charging, like a magnet, receiving
it at the antigrav factory, and that discs of
the material can then be installed in a ship and activated merely by
flipping it over as one might flip over a mirror, until replacement is
required. (See also the addendum section on antigravs.)

Put simply, the point is that there's no way to know how antigravs
work. Our friend Occam is silent on the matter. What little we do know inasmuch as pushing against gravity
fields suggests something as simple as a gravitic sail or mirror or the gravity
equivalent of a ceramic superconductor. Unless and until we know
more, assuming that the ship is magically putting out all the energy of
a rocket's thrust without rocketry seems a little odd.

Speaking of which . . .

5. Engine Thrust

Even
engine thrust isn't necessarily based directly on reactor energy.
If
they're all carrying around rocket fuel, for instance, this fuel could
be burned directly for thrust, and the reactor could only be drawing
for electrical systems, just as in the space shuttle.
Alternately, the fusion fuel supply could be fused
separately to form fusion rockets, which would have no real impact on
main reactor energy . . . the reactors at that point would be running
assorted electrical systems but only have a tangential relationship to
the engines.

Given the apparent central location of a specific "engine
room" on
Venators which also feature scattered thrusters along the stern, as
well as the presence of a Munificent's main reactor
compared to its many external thruster engines, then it seems that we
cannot
presume that the reactors are actually placed near the engines to serve
as fusion rockets directly spitting out the fusion exhaust, but that
instead they are separate. The thrusters could of course have
their own fusion reactions afoot in separate reaction chambers.
This would explain a peculiarity of Star Wars ships, in
that whenever
a ship is 'alive', whether or not it is accelerating, its engines are
almost invariably lit brightly. Fusion furnaces require
intense
temperature and/or pressure to function . . . keeping the engines hot
and ready to go, even if this is wasteful of fuel during constant
'idle', could be a necessity.

Alternately,
however, the running engines could simply be some sort of thermal shunt
for the main reactors. This concept is not without merit,
given
that from what we've seen thus far there's no evidence for separate
engine function. That is, we have not seen individual
engines
shut down, except when blown apart by battle damage as occurred to an
Acclamator in "Innocents of Ryloth"[TCW1]. When the ion
cannon
shut down a Star Destroyer in orbit of Hoth, its engines all powered
down simultaneously. If all the engines were tied to the same
reactor or had some other similar single point of failure (e.g. the
oft-mentioned "power converter" of unknown use), this would make sense.

What we do know is that Star Wars engines are generally ion
thrusters. The ANH script refers to X-Wings as having "ion
rockets", and the TESB script refers to the Falcon's "ion engines".
The TESB novelization refers to the ignition of the Falcon's
ion engines, in reference to starting up the thrusters from a darkened
state after the ship detached from the ISD. And, of course,
the RotJ novelization explains that TIE fighters are Twin Ion Engine
vehicles. Perhaps most importantly, given that all the other
examples refer to very small vessels, the Revenge of the Sith
novelization suggests that ion engines are the technological basis of
even the bigger ship engines: "The shimmering canopy of
ion trails and turbolaser bursts was fading into streaks of ships
achieving jump as the Separatist strike force fled in full retreat."

Whereas most rockets operate by burning or annihilating
something in order to produce high-pressure gasses which are then
directed out of a nozzle, producing thrust, ion engines operate by
taking a charged propellant and, via electrostatic or electromagnetic
fields, causing the propellant's rapid departure. Soviet-type
Hall Effect thrusters, for instance, trap
electrons in a magnetic field, and as propellant is fed in the electron
collisions ionize the propellant, which by the design of the engine
ends up departing at high velocity, taking some electrons with it,
producing a net charge for the escaping gas of zero, though the plume
is somewhat disorderly.

While Star Wars engines may not be Hall Effect based (though
there are resemblances), the general point of an
electrically-accelerated charged particle thruster seems to be the
case. This can serve to help constrain our ideas on possible
engine-reactor relations.

For instance, just as steam is produced by modern naval
reactors, charged particles (plasma) may be the design goal of Imperial
reactors, fusion exhaust product particles which can then be
transferred to the engines as propellant and converted to electrical
power by special generators. Or, the entire reactor system
may simply create electricity, with engines electrically powered and
separate propellant unrelated to the fusion activity on hand.
Or, the reactor may be electricity-oriented, with the fusion
fuel available for use as propellant via fusion exhaust or turbines,
with electromagnetic acceleration of the products. Or, the
propellant is simply a coolant for the reactor, and is accelerated away
from the ship thus providing thrust and thermal control. (Given the seeming afterburn activity of the Falcon during a
moment of maximum thrust, not to mention the seeming flame from the
Invisible Hand when using thrust deflectors, it may be that the ionized
propellant can be genuinely ignited, as well, though this is uncertain.)

Given the aforementioned simultaneous engine failure when the
ISD was hit by ion cannon shots in TESB, it seems likely that the
electrical system of the ship is a single point of failure for the
engines. The "power converter" is thus probably the
electricity generator fed from the reactor, and which in turn feeds the
power to the ship. The power source for the generator may,
like the Naboo generator in TPM, be reactor plasma. The
propellant identity is unclear, but in any case there is a relationship
between engine thrust and reactor power.

So now we've got something.

B.
Discussion

Curtis Saxton argues that a Star Destroyer's engine glow must
represent thermal power emission. While this is true to an
extent, the claim can be taken too far. Quoting the claim:

"The idle power of a starship's engines
(i.e. when the thrust streams are effectively
halted)
can be estimated from the power of the thermal glow visible through the
engine aperture
(of area A).
If σ is the Stefan-Boltzmann constant
and T is the effective temperature of the
radiating surface,
then the radiated power is P = A σ T4.
For example, if a star destroyer has three online engines in which the
glowing surfaces have 100m diameters,
and where the glow is yellow (temperature ~ 5000K),
the ship must have an idle engine power of at least
8 x 1011 W."

This represents a minimum claim of 800 gigawatts.
But, there are multiple problems with this argument.

First, the calculation requires us to believe that the entire
engine bell
interior is glowing hot, rather than the central aperture from which
the propulsive gases are coming. Second, as we've seen in
Attack of the Clones, the entire inside of the engine bell is not
glowing due to heat, but due to glowing gas being directed along
it. It is logical to presume the same of Star Destroyers.

Even present-day ion thrusters might generate glowing gas, but
the gas is so diffuse that although the ions are incredibly hot
individually, the gas temperature is fairly cool. Given that
we seldom if ever see a great deal of heat distortion (some occurred in
AotC, but not much considering the size of the engine bells), it hardly
follows that the engine bells are white-hot. Rather warm, yes.

It's also been claimed at StarDestroyer.Net that a Star
Destroyer reactor has a peak power generation in excess of 1E25
watts, or about ten trillion terajoules per second. However, this is
nonsense, since to achieve that power level with a fusion reactor would
require fusing almost 200,000,000 metric tons of
deuterium in one second. To get a sense of that, suppose they stored it
in the form of lithium
deuteride at 12 times its normal density (much more and you'll risk
fusion via compression). Stored thus, that fuel would fill a
container of 1000m x
142m x 142m, or almost half of the internal volume of a 1600 meter long
Star Destroyer. That's for one second, and it would
have to fuse all at once!

At StarfleetJedi.Net, it's been suggested that the hyperdrive
limitations
of not being able to be activated near a planet are indicative of power
requirements in the exawatt range. Quoting the claim:

"If the minimum distance to jump to
lightspeed away from a planet is at
some local value of g,
beyond
which the hyperdrive may not develop sufficient power, then we can
calculate the minimum power of the hyperdrive system, by rate of change
in gravitational potential, as mgc.
For one planetary diameter from the surface of an Earthlike planet,
this is ~357 megawatts per kilogram {of ship}. For 6.5 planetary
diameters, this
is 17 megawatts per kilogram."

However, this argument is also a bit peculiar, since there's
no indication in the canon that the hyperdrive activation limit is
related to power consumption. If that were so, then it
wouldn't make sense for it to be a universal rule for all ships, as is
suggested in the canon. Specifically:

"This served as clearance radii for the effects of
the simple
antigrav drive which boosted all spacecraft clear of the gravitational
field of the planet.

The mathematics of spacedrive were simple enough even to Luke. Antigrav
could operate only when there was a sufficient gravity well to push
against-like that of a planet-whereas supralight travel could only take
place when a ship was clear of that same gravity. Hence the necessity
for the dual-drive system on any extrasystem craft." (ANH Ch. 7)

Elsewhere in the ANH novelization we learn that antigrav range
is six planetary diameters, but again, there's no indication that it is
different for different ships. Gravity tugs on all vessels
equally.

Further, obtaining an exajoule per second by fusion
is a costly affair. Per certain values for D-T fusion, it
would necessitate about 3000 kilograms of fuel per second.
Going by
the maximum energy density for the diesel fuel suggested on that site,
it
would still require 3500kg/s, or by volume over
4300 liters (4.3m³) per second. Even if we assume a Star
Destroyer's fuel capacity is 10% of her volume, then at such
consumption rates she would burn up her fuel in just two weeks.
And
while a Star Destroyer is naturally rather unlikely to be making
hyperjumps from planetary orbit a million times in a two week period,
the concept that the ship could suck 4300 liters of fuel and then just
sip it the rest of the time (i.e. using thousands, tens of thousands,
or hundreds of thousands of times less fuel for standard operations)
seems a peculiar one.

C.
Engine Power Examples

Since no other good information on power requirements exists,
we can
take thrust examples as a guide. However,
whereas Saxton and friends seemingly use completely made-up
acceleration values, we'll study the canon itself. There
are a few examples which might give us something to work with.

1.
TCW and Anakin's Ram

One example of Star Destroyer acceleration can be borrowed
from the
Venator Class as seen during the Clone Wars ("Storm Over
Ryloth"[TCW1]).
With engines boosted for a collision course, we get what
ought to be a good example of future Imperial
ship performance, barring some absurd advancement that renders all
prior vessels sitting ducks.

Note,
however, that the planet was not terribly distant in this example,
meaning that antigrav use could've been involved, in principle.
However, since antigravs are presumed to allow greater
performance, and since the context of the scene is not indicative of
antigravs, we'll see what we get.

a.
Determining Acceleration

The vessel in question is the
cruiser Defender, and the damaged Defender arrives in the system via
hyperdrive
at an eyeballed range of about 60 kilometers from the opposing Trade
Federation battleship, closing at around a couple of hundred meters per
second. Two minutes of screen time later, the Defender has
closed to within an eyeballed range of ten kilometers, still moving
forward but at a slow rate. Moments before the trap is
sprung, we
see the following image:

The 550m wide Venator takes
up about 17% of the image width, meaning it would take 5.78 of them to
fill the screen. Assuming a total field of view of between 30
and
60 degrees, then, the Venator's angular width is between 5.2 and 10.4
degrees. Using the methods from the range pages:

This
gives us a range between five and seven kilometers . . . close, but not
as close as we're used to on the range page. Presumably this
is
due to the CGI. However, we do get overlap in the higher
ranges,
so five to seven kilometers seems likely, both by calculation and
eyeball estimation.

The engines are boosted and the ship begins
lumbering toward the Trade Federation battleship. About 55
seconds later, impact occurs with the outer ring of the battleship
(which of course is several hundred meters from the bridge).
At
that time, an eyeball rate of speed is perhaps as high as 550 meters
(about half the ship's length) per second. Assuming a full
run
of 7200 meters (about the maximum distance noted) and a start from zero
relative velocity, then the 55 seconds to impact requires an average
velocity of 131 meters per second. Assuming linear
acceleration,
that would result in a final velocity of 260 meters per second, with a
very poor acceleration of 4.75m/s², or about half a gee.
Given the approximate eyeball rate of speed, however, we
could
presume a higher acceleration at some point in the run. For
instance, 55 seconds to get from zero to 550m/s would give us an
acceleration of 10m/s², or approximately 1g.

However,
that seems perilously low, even for a damaged Star Wars cruiser.
The acceleration
rate of the Millennium Falcon with an afterburner boost
was 210 m/s², or
about 21.5g,
which is 20 times that figure. And after all, the Trade
Federation
ship couldn't stop the Defender,
and if the Trade Federation ship had the ability to reverse thrust for
even a tenth of the Falcon's maximum forward acceleration, it could've
reversed and escaped fairly easily. Instead, the Trade
Federation ship simply sat there and took a kilometer-long knife right
in the face.

The best-case thought is that the Defender's
acceleration was slowed by tractor beams, and that "we can't stop it!"
as stated by the droids referred to the tractor beams being
overwhelmed rather than the obvious and ordered weapons fire having
little effect. However, it would've taken a moment at least
for
the Trade Federation ship to react to the acceleration, and the initial
acceleration of the Defender was no higher than what we would expect
given the speeds seen.

Also
in fairness, the Defender was damaged, though no direct
engine damage is apparent, and indeed a ship with engines too heavily
damaged would've been useless for Skywalker's plan. In other
words, if Skywalker planned to ram but the Defender's acceleration
ability was a miniscule fraction of what a Trade Federation warship
could normally muster, it would be the equivalent of one ocean-going
battleship trying to ram another by having the crew hop into the water
and push . . . an absurdity.

Nevertheless,
let's assume that most of the talking scenes on assorted bridges were,
in fact, overlapping data. This gives us a time of about 29
seconds to get to 550m/s, for an acceleration of 19m/s².
Interestingly, this also corresponds with another value . . . if we
take the 7200 meter run and average the speed to 275 meters per second,
then our straightline acceleration would be 21m/s² for a time of 26.2
seconds. Given that these two separate values correspond so
well, we can use 21m/s² as the correct figure.

Note, however, that reverse thrust is probably not as good at
all . . . after all, in The
Empire Strikes Back
two Star Destroyers
passing in the night struck each other, apparently unable to directly
slow themselves from a relative velocity of something like 200 meters
per second! Even just counting from the moment when we were
first
shown them both in the same frame at less than a kilometer apart,
that's a full ten seconds during which they failed to avoid collision.

Similarly, when the Invisible Hand started falling toward the
Coruscant surface in Revenge
of the Sith,
it was all the ship could do to level herself again. The ship
fell for 10 seconds, then after 20 additional seconds featuring orders
to reverse stabilizers and magnetize, the "emergency booster engines",
which seemed to just be thrust reversers on the main engines, were
finally fired. It still took almost another whole ten seconds
for
the vessel to level out. In low orbit, the gravitational
force on
the vessel would have still been below 1g,
but not terribly much less. Even if we presume the vessel was
dropping for the full 30 seconds and took 10 to stop the descent, then,
the ship's main engines on full reverse would've offered no more than 3g, and probably
less.

b.
Guesstimating Power

So, let's
assume that it started from zero. Given a middle-of-the-road
Star
Destroyer mass estimate of 40 million tonnes and a very rough
estimation of the mass of the much less voluminous Venator at somewhere
in the 10-15 million tonnes range, that would give the vessel a
kinetic energy of .5 (15000000000) (550²), or about 2,270 terajoules.
Considering the acceleration rate, then this would represent
a
peak engine
power of around 87 terawatts.

If
we
assumed 75% of reactor power could go to engines and assumed engines
that
were 90% efficient (higher than current ion engine technology, mind
you, but not impossible), then the value for peak reactor power would
end up as
about 120 terawatts.

c.
Translating to ISD

Now,
the above is the only demonstrable value we have from this, however
back-of-the-envelope and such it might be. But, given
that we also ought to
presume, based on all the evidence, that a Star Destroyer can basically
keep up with a fleeing, weaving, non-afterburning Falcon, then that
would still seem a slow figure. Even if the Falcon without
afterburn
was only capable of half of her maximum acceleration (i.e. 100m/s²),
the weaving and bobbing
probably wasn't removing that advantage by a factor of ten.
So
a Star Destroyer is probably capable of 25-50m/s² or so.

So, if we went with the full-size Star Destroyer and our
selection of a 25-50m/s²
acceleration rate, then for a 40 million tonne Star Destroyer to reach
the same velocity would involve a kinetic energy of 6,050 terajoules.
At the acceleration rates given, this would require either 22
seconds or 11 seconds, corresponding to an engine power of 275
to 550 terawatts. Using the reactor power percentage and
engine efficiency assumptions above, the peak reactor power of a
Star Destroyer would thus come out to 380 to 750 terawatts.

Considering
that the Imperial is roughly three times larger than the Venator by
volume, the former value of around 400 terawatts might have a bit
firmer
footing, but one's terawattage may vary.

2.
TESB Star Destroyers Comin' Right At Us

Another possible acceleration example occurs in The Empire Strikes Back.
Based on this
section
of the weapons range
page,
we
see a pair of Star
Destroyers moving at about 30 kilometers per second relative to the
Falcon and its closely pursuing Star Destroyer, the Avenger, shortly
before its 90 degree dive toward the asteroid field. Ten
seconds
of screen time later, the two Star Destroyers are visible as the Falcon
dives away, with Avenger right behind. The vessels at that
point
are moving at a relative velocity of perhaps a hundred meters per
second, or effectively zero compared to the earlier relative velocity
of both pairs.

Unhappily,
it seems that this example is probably unusable. At minimum,
this
would require that both pairs of ships (two ISDs and the Falcon with a
trailing ISD) decelerated at 1500m/s², which would require 75
kilometers of stopping distance, which happens to be the total distance
scaling
from the weapons range page. However, that would have both
pairs meeting at 37.5 kilometers while still moving quickly, and thus
we must double that deceleration value.

Thus we find some confusion, since 3000m/s² is also more than
14
times the afterburning forward acceleration seen by the superfast
Millennium Falcon. If we took this as a valid example, it
would
be a profound outlier from all other examples in the visible canon,
including those from Star
Wars: The Clone Wars.
It would also be a profound outlier from the collision a few
seconds later, apparently unavoidable despite a relative velocity of
around 200 meters per second! If the ships really could
decelerate at 3km/s², then they could've stopped in less than a tenth
of a second!

However, it would
be within the normal range of decelerations
observed when vessels exit hyperspace. Thus, I would submit
that
this example is probably an example of arriving warships dropping from
hyperspace and almost
arriving right on top of a battle, whether by accident or design.
A similar tactic has been
intentionally used in the past, as seen when Anakin exited hyperspace
in a shuttle in such a way as to almost kiss the hull of an enemy ship
he planned on docking with ("Grievous Intrigue"[TCW2]), not to mention
the somewhat frequent Separatist technique of hypering in on top of
foes ("Ambush"[TCW1], "Storm Over Ryloth"[TCW1], et cetera).

3.
Ships on the Ground and in the Air

Non-acceleration examples might also work. For
instance, Acclamators land on Geonosis in Attack of the Clones.
Palpatine and other government officials observe the
departure
of Acclamators at the end of the same movie. In The Clone Wars,
vessels land, take off, are boarded mid-flight in the atmosphere in
battle ("Jedi Crash"[TCW1]), and other similar things all the time.

In most such cases, unprotected individuals are within
kilometers of the ships, if not directly touching them. In
the case of Palpatine, he was seemingly in the line of fire of the
engine exhaust. This tells us that the heat dissipation of
these vessels, be it from their engines or their hulls or any heat
sinks thereon, cannot be terribly excessive. How does this
help us? Well, if
this is the maximum energy pouring
out of the tailpipe or otherwise being released from the vessel, and if
we presume a certain efficiency of the ship's systems (even, say, 99%),
then we can have an upper bound for the reactor energy at the time.

Using information from the legendary Nuclear Weapons FAQ, we find an
easy method of calculating the range at which one can expect first
degree burns from a nuclear weapon. Unfortunately, of course,
this is a ballpark figure. While exhaust from a
rocket engine will be different inasmuch as the specific relative
percentages of energy emission (e.g. blast versus radiation versus
thermal effects), we should have a decent guesstimate of the maximum
energy coming out of the back of those ships at any given time.
This guesstimate will be imperfect, of course, given spectral
issues, but at least it's something.

As it happens, even a nuclear weapon of a single kiloton
is enough to produce first degree burns at 1.2 kilometers.
Per the FAQ author's own chart, 4.3 kilometers is the range
for first degree burns for a 20 kiloton device. In both
cases, of course, this is for a single energy release event -- a
bomb going off -- and not sustained exposure. The true
output from the vessels would thus be far lower.

Eyeballing the Palpatine incident, we can estimate that his
range from the ships was on the order of a couple of kilometers.
Overestimating, then, based on the single-event bomb
detonations
(rather than fully correcting for sustained energy release), we'll say
that
the engines would be limited
to a kiloton, and probably a lot less given the even closer clones.
100 tons . . . one-tenth the bomb value . . . would probably
be closer to fair, though still high.

At 99% thermal efficiency, then, the reactor must have an
output no greater than 10 kilotons per second, or about 42 terawatts.
If the ship's efficiency is more like 90%, then the reactors
fall to a mere kiloton per second, or 4.2 terawatts. To
be sure, even that last value is nothing to sneeze at . . . it is one
quarter the total energy per second used on the entire planet Earth as
of 2006.

D. Conclusion

It
is interesting, to say the least, that the usable examples above (1 and
3) roughly correspond to one another, even given the overestimations in
both cases. Considering that they are based on independent
criteria (acceleration in one case, thermal radiation due to perfectly
normal efficiency ideas in the other), the fact that both agree on
something
close to low-to-mid terawatt range power levels for Star Destroyer-type
vessels is interesting. More interesting is that
the first example occurs near a planet, and thus might be even more of
an overestimate if antigravs were involved at all.

If we were to roll with these examples even in spite of that,
we could go for Acclamators and
Venators in the 80-120TW range, and a 400-500TW Imperial Star
Destroyer, without problems too severe. As
noted
previously, though, this is only an intriguing possibility . . . it is
entirely
likely that none of these potential examples are completely valid.
For
instance, technology to deal with thermal inefficiencies in ways other
than simple radiation . . . such as the intriguing science fiction idea
of dispensing heat via neutrino-based or similar technobabble radiation
systems . . . would nullify the third example. And, it's
possible
that a ship at full engine 'burn' can actually output almost all of its
reactor power to the engines, depending on the situation.

Generally speaking, though, it seems best to assume that the
majority of the vessel's waste heat is emitted through the engines.

V.
Conclusion

Star Wars vessels operate via nuclear fusion, fed through some
sort of liquid fuel (possibly called tibanna) with characteristics not
wholly unlike a hydrocarbon fuel (such as the "diesel starship" idea
fielded elsewhere). The fusion reaction or reaction cycle in
use is not clearly indicated, but there does seem to be a great danger
of the reactors overloading and exploding if sufficiently damaged.
This is unlike most current fusion reactions of interest on
Earth, implying either a reaction cycle that we know and have
discarded, one we know but believe safe due to other constraints the
Empire does not follow, or a reaction cycle that is completely unknown
to us and which cannot be made completely safe, but with the benefits
outweighing the risks.

Reactor energy is fed to one or more "power converter"
generators, possibly via plasma, which the generators convert to simple
electricity. This electricity is distributed via conductive wire in
most cases, though occasional use of photonic power transmission is not
unknown in large-scale applications (e.g. the second Death Star, which
would presumably have other true "power converters" on hand to go from
photonics to electronics).

This electrical system powers her ion engines, though damage
to the latter can overload the power converter(s).
The nature of the propellant for the ion engines is
not certain (it could be the same liquid fuel, or some special
as-yet-unknown solid mass, or reactor coolant, or reactor plasma.)

Based on assorted power requirement calculations, it would
appear that the Clone Wars era warships of the Republic were probably
limted in reactor power to 120TW or below, with the Venator being the
largest and most powerful ship in that criteria. The far
larger Imperial Star Destroyers, assuming similar technology, would
figure somewhere in the 400-500TW range.

VI.
Addenda

A.
Running Some Numbers

Just for kicks, let's assume, for
the moment, that what the non-canon commonly labels as the "reactor
bulb" on the ventral side of an ISD (circled at right) is, in fact, the
fuel tank, and that the small portion we see is actually part of a
sphere. This would give us a ~200m fuel tank on an
ISD, assuming it is 1600 meters in length. 4/3r³
tells us that this would give it a volume of 4,200,000m³, the
equivalent of over 2000 space shuttle external tanks (at 2070m³) filled
to capacity. While that sounds like a big tank, it
only represents 7.8% of the internal volume of the vessel.

First, let's assume that this is
just your basic fuel tank, with deuterium for fusion stored there in a
liquid form. The density of liquid deuterium is reported
variously, but normally falls within a few points of 165
kg/m³. So, given a tank as specified, the Star Destroyer
could hold some 691,150 metric tonnes of liquid deuterium.
(Liquid deuterium would make sense under most circumstances
provided you could readily chill deuterium to around 20 degrees
Kelvin. You could even go for solid deuterium if
you knocked off just a few more degrees. And unlike on modern
Earth, where cooling hydrogen into liquid would require energy in order
to keep it cool, in space all you'd need to do is keep it exposed a bit
(as one might do with that hemispherical bulb), so at least in part
it's cooled for free.)

For the below, we'll assume the
form involving six deuterons and 43.2 MeV, being among the more
powerful fusion cycles.

1.
Joules per Gram

Now, we need to get from
mega-electron volts to a more useful value for our purposes.
The way to do this is to employ Avogadro's number, the number of atoms
in a mole of material. A mole of an
element features a known number of atoms resulting in an amount of
material which, in grams, equals the numeric value of the atomic
weight. In other words, a mole's worth of carbon-12
is 12 grams, and a mole's worth of hydrogen (with an atomic weight of
1) is 1 gram. The atomic weight of deuterium is 2.01355, so a
mole's worth has a mass of 2.01355 grams. Avogadro's number
is 6.0221415E^23, or 602,214,150,000,000,000,000,000.

So, in order to find out the number
of deuterons per gram, all we need to do is to divide Avogadro's number
by 2.01355 grams. The result is a "mere"
299,080,802,562,638,126,691,663.9765 deuterons. If we then
divide this by six for each deuteron burned up in the deuterium cycle,
then the result is 49,846,800,427,106,354,448,610.66.

What has that got us?
Well, for each sextet of deuterons, we were making 43.2 MeV.
Thus, a gram of deuterons makes that energy times the
almost-50-sextillion sextets. The result is
2,153,381,778,450,994,512,179,980.63 MeV, which converts to
344,993,294,752.66 Joules, or 0.34499 terajoules.

Not bad for a gram of heavy
hydrogen. And yes, the figure is artificially-specific given
my total skipping of
significant
digits, but they annoy me and this is a hobby. So
sue me.

2.
Total Energy

0.34499TJ/g means that for a
kilogram of
deuterium, we're looking at 345 terajoules, which the Star Destroyer
could use assuming 100% efficiency. Of course, that would be
a
silly assumption.

If the Star Destroyer has a fuel
tank capable of storing 691,150 tonnes of deuterium, then the total
energy possible from that tank of fuel is 238 billion terajoules,
2.38E23 Joules, or almost 57,000 gigatons of energy . . . more than
enough to allow one to hold a massive barbecue. However, a
Star Destroyer can't just go fusing all its deuterium at
once. Were it to do so it would quite rapidly end up a ghost
ship as anything requiring energy (such as life support, propulsion
systems, et cetera) came to a sudden and grinding halt after fuel
exhaustion.

3.
Endurance of a Star Destroyer

The question, therefore, is how
long one would expect a Star Destroyer to be able to endure without
hitting a gas station.

The question can readily cause one
to tie oneself in knots, if pondered too carefully.
But if we assume that a Star Destroyer must be away from refueling for
a year, then the average power consumption would
have to be the total terajoules divided by 31,536,000 seconds, which
results in 7561 terawatts, or about 1.8 megatons per second.
That's about 7.6E15 watts. That would represent the
consumption of 21.9 kilograms of deuterium per second in one or
multiple reactors. In any
case, we're talking about the fusion of several kilograms of deuterium
per second, which is at least plausible given large or multiple
reactors. Fusion thus fulfills the power
requirements of Star Wars quite nicely.

Now, if you recall our earlier estimate of 400-500
terawatts for maximum reactor output, then the likely endurance of a
Star Destroyer before hitting a gas station would be a much more
impressive 15 years, on par with the fuel reserves of modern aircraft carriers.

B. Antigravity and the Perpetual Motion Counterclaim

As we understand
physics, of course, almost none of these cheats we see in science
fiction are even remotely possible. Antigravity, for
instance, is
often said to theoretically allow for a free-energy perpetual motion
setup. The rationale is that an antigrav system requiring
less energy
than what would normally be expended to raise an object in a gravity
field could, if turned on and off at will, allow a generator that can
recover the energy of motion of a falling object to get virtually free
energy, an energy profit over and above what would have to be put back
into the antigrav unit. Such generators are not unknown . . .
falling
water generates electricity in hydroelectric dams, for instance, and
the atmosphere is kind enough to move the water back above the dam to
start the process over again.

The issue is conservation of energy, which along with conservation of
momentum is encapsulated in relativity as the conservation of the
four-momentum. Locally, from the perspective of the dam, the water is
free energy. Globally, however, the sun and atmosphere are doing the
work of getting the water back above the dam.

"But,"
you say, "a natural magnet can perform levitation tricks without energy
input!" This is true, but this is merely an effect of the
stored energy within the
magnet, energy which is expended when the
magnet is used to move or deflect an object. Similarly, a
quick search
of the internet will show you hundreds of ideas of how to generate
perpetual motion and free energy from magnets, Earth's magnetic field,
vacuum energy, zero-point energy, the Casimir Effect, and other natural
or environmental factors. None of it is actual free energy, and
most of it isn't worth the time to consider anyway even if you can get
energy out of it, especially given the nature of the salesmen.

Free energy salesmen usually explain
how assorted conspiracy-theory-nut groups like the Illuminati, MJ-12,
Lizard Men, or Big Oil are suppressing them, which should give you a
sense of how much stock to put in the claims, and why you should
probably not
search the
internet for such things if your mental health is important to you.
Just as people peddled elixirs of life back in the old days,
"New Age"
medicine now claims to have evolved past Western science and will
prescribe you all sorts of 'natural' drugs/supplements that it would
take medical professionals awhile to decode the full effects of, though we already know they don't do much good.
Similarly,
these New Age "scientists" claim to have evolved past modern physics,
and just need your money to be able to build their machines to solve
the problems of the world, and to escape Big Illuminati-12 Lizard Oil
or whoever.

While most theories of perpetual motion are too
simple, ignoring/masking the effect of some basic physical phenomena,
some of the ideas almost sound good, and have befuddled more than a
few intelligent people. Some have even required extensive
calculations
by professional physicists to debunk.

Likewise,
I can't help but
think that such objections to science fiction antigravity (or, for that
matter, FTL propulsion) on the grounds that a perpetual motion machine
would develop are, like all other theories of perpetual motion,
similarly too smart by half. In the case of Star Wars antigravs
that push against a planet's gravity well, we can come up with a lot of
theories. Earlier, we pondered a material that allowed
antigravity to occur, and my personal favorite idea was a disc of this
material that, suitably charged by whatever means, could simply be
flipped over to push against the gravity field, and used for propulsion
by tipping it just so, like a gravitic mirror. The material
itself might wear out over time, and of course its charge of whatever
stored energy would be involved would slowly be lost over time.
This would not be a perpetual motion device . . . you could use it to
get energy for awhile, but then it would be dead.

Of course, something far more exotic might be the case, or it could be something more mundane. Either way,
the
simple fact is that in the canon, perpetual motion apparently doesn't
exist. Ergo, the science fiction technologies we see in use
cannot be
used to create it. But that still does not prove that antigrav and other technologies do
not cheat the energy requirement for such things as getting to
orbit (whether locally or, pardon the pun, globally), just as
hyperdrive cheats the universal requirement per modern physics that infinite energy is required to go
faster than light.